Musnad Abu Ya'la al-Mawsili 159:61

Wahb ibn Baqiyyah narrated to us, Khalid informed us, from Abd al-Rahman, from Abu al-Zinad, from al-A'raj, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "If one of you asks his brother to place a piece of wood in his wall, then let him do so."